1. Technical Field
This invention pertains to escalators in general, and to escalators driven by step chains in particular.
2. Background Art
Escalators are a known method for conveying people from a first elevation to a second elevation. Typically, an escalator includes a frame, a drive, a step chain and a pair of balustrade assemblies. The frame comprises a truss section on both the left and right hand sides of the frame. Each truss section has two end sections forming landings, connected by an inclined midsection. Matching pairs of roller tracks are attached on the inside of each truss section, i.e. the side of the truss section facing the other truss section. The upper landing usually houses the escalator drive between the trusses. The drive powers a pair of step chain sprockets, which in turn impart motion to the step chain. The step chain travels a closed loop, running from one elevation to the other elevation, and back.
Step chains typically consist of a pair of chain strands connected by a plurality of axles, each axle having a pair of rollers which contact the roller tracks. The chain strands are attached to the axle inside of the rollers. Each strand is formed from a plurality of chain links. Each link has a pair of side plates spaced apart from one another, pivotly attached to the side plates of the adjacent links of the strand. This link arrangement is repeated as many times as is necessary to arrive at the length strand, and therefore the length chain desired. The axles connect every "n.sup.th " link in one of the strands to the aligned link in the other strand. Connecting the strands with the axles ties the two independent strands into a single step chain.
The load on each step chain axle may be described as having two main components: the load on the attached treadplate and the load transferred through the attached chain strands. The load attributable to the attached treadplate is simply the weight of the treadplate and whatever load is on that treadplate. The axle receives this load where the treadplate is attached to the axle, inboard of the rollers. The load attributable to the attached chain strands, on the other hand, is a function of the step chain sprockets pulling the chain, and therefore includes a percentage of all of the individually loaded treadplates, along the inclined midsection. Both of these loads on the step chain axle are transferred to the rollers attached to the axles, outboard of the chain strands. Each axle, therefore, can be viewed as a beam simply supported at each end by a roller. The chain strands and the attached steps, both inboard of the rollers, can be viewed as loads on the beam. If the loads are great enough, the beam will deflect due to the position of the loads on the beam.
A person of skill in the art will recognize that while a step chain may be constantly loaded, the load on each step axle will vary depending on the position of the axle along the circuitous path taken by the step chain. Specifically, it is known that a particular step chain axle will experience a greater load in the transition area between the inclined section and the upper landing when the exposed side of the step chain loop is traveling up the incline, than it will in any other section of the step chain travel path. As a result, the step axles deflect a greater amount in this area, thereby causing increased wear on the axles and bearings supporting the rollers.
The undesirable axle deflection can be eliminated by using larger axles, or by using axles fabricated from stronger materials. These solutions, however, increase the cost of the step chain significantly. Moreover, in many cases these solutions are not practical for existing escalators. What is needed, therefore, is an apparatus for supporting the step chain of an escalator.